Having previously demonstrated immune responses in human subjects to heat labile enterotoxin of E coli and the colonization factor CS6, when administered via the transcutaneous route, this application proposes a clinical plan to determine if the observed immune responses are relevant, functional, and protective. First, a preliminary Phase 2 clinical study is proposed to firmly establish the antigen/adjuvant dose required to achieve a consistent and robust immune response. This will be followed by a second study in which volunteers will be challenged with a live E coli organism that expresses both LT and CS6. A successful demonstration of efficacy will lead to further development of an ETEC vaccine with broader coverage.